On Friday morning, the lobby of the Brampton courthouse was bustling with lawyers and their clients, jury members and court staff.

Const. Mike Klarenbeek, 53, was among several Peel Regional Police officers manning the security checkpoint, just inside the double doors to the imposing glass building. It is a hectic area, where those seeking entry are ushered into two lines, separated by a grey velvet rope.

What follows is a reconstruction of the chaotic hours that ensued. It is compiled from on-the-ground reporting, official statements and witness accounts, some of which could not be independently verified.

At 11:01 a.m., a well-dressed man, who some witnesses described as wearing a black trenchcoat, tried to get in through the lawyer’s entrance.

“Sir, can you come here?” one of the officers asked, before the man pulled out a gun.

One lawyer said she heard the shooter talking to police at the security check. Moments earlier, he had held the door open for her.

“He wanted to enter the building under the pretense that he was a lawyer,” she later recalled, welling up. “He pointed a gun at the police officer. He could have shot anyone.”

He opened fire, hitting Klarenbeek, before an officer, it’s unclear who, shot him down. At least five uniformed police officers surrounded the shooter, who was handcuffed as he lay face down on the ground. He was later pronounced dead.

WARNING: GRAPHIC CONTENT. Dramatic cellphone video has surfaced on Facebook from the Brampton court shooting. It was posted by user Arslan Hanif.

Bystanders in the hallway crouched behind a wall or lay flat on the floor of a corridor. There was panic in the nearby cafeteria. As the shots rang out, a woman ran in, yelling “Guns! Guns!”

A few people ran down a hallway, only to find themselves stuck in a corner. “There was no way out,” one woman recounted. “There was no door, and I just thought, ‘My life is over.’”

Criminal defence lawyer Will Jaksa sent his first tweet at 11:03: “Gun shots in Brampton Courthouse. We’re locked down in Court.”

Two minutes later, reporters at the Star newsroom received a forwarded email from Toronto criminal defence lawyer Corey Nishio.

“Police officer shot in . . . Brampton court house” the subject and body of the original email — sent just a minute earlier — read.

Within minutes of the shooting, the courthouse was in complete lockdown. Court proceedings were abruptly stopped, including a mock trial being conducted by a group of more than 40 students from Peel Region School Board and four staff.

For those in the courtrooms on the second floor, not even trips to the bathroom were allowed for a time, as officers swept the sprawling building.

At 11:16, Klarenbeek was whisked out on a stretcher, surrounded by paramedics and a fellow officer, who appeared to be applying pressure to the wounded man’s torso.

At first, officials at Peel police and EMS were sparse with details, only saying a “major incident” had occurred.

But by 11:49, Peel police confirmed to media what those on the scene already knew: one of their officers was involved. At noon, police said the officer, who had been taken to Sunnybrook Hospital, was in critical condition. His condition was later upgraded to stable.

The fire truck, ambulances and police cruisers were soon joined by a SWAT team, which filed into the lobby. Three police dogs did a perimeter check before being led inside. The Special Investigations Unit, which probes serious injuries involving police, also arrived.

In the parking lot, police searched a silver Chrysler Sebring.

Waiting in lockdown, those inside the courthouse posted updates on social media, called loved ones and reflected on the frightening experience.

One courthouse employee said she was in the elevator on her way to the ground floor when the shots were fired. When the doors opened she saw one man lying in a pool of blood.

At around 2 p.m., police began interviewing witnesses and taking down names, phone numbers and addresses on the second floor, before allowing them to exit down a stairwell and out a side door.

Those hoping to hit the road after a difficult day were met with a long wait, as police again checked the identification of everyone leaving the lot.

While they waited for the lot to clear, some stood outside their cars, talking quietly in the light rain.